How to troubleshoot failure of some services or no audio on a telephone after installation and wiring?

If some services fail or a telephone has no audio, first confirm the paired configuration of the devices at both ends and that the patch cord terminations of the optical ports are in good condition, and check the received optical power margin; then check the service-side wiring and the interface card type, and on the E1 side check whether the bit rate of 2.048 Mbps, the HDB3 line coding and the 75 Ω/120 Ω impedance are consistent with the opposite end, while on the telephone side check the voice channel port markings and the wiring sequence; then check whether the non-blocking time-slot cross-connection configuration between the 2 groups of E1 and the subscriber interfaces has taken effect; finally confirm that the DC-48V or AC220V power supply and the grounding are normal. For maintenance, it is recommended to switch off the power before plugging or unplugging the service cards and the optical ports, to clean the end faces regularly and to re-measure the optical power; if it still cannot be recovered, it is recommended to contact the manufacturer's technical support together with the device alarms.